Paperwork = Cash payment.
Pay at the start, once you are sure that the girl is the one you booked and that you want to stay. Any issues, pat your pockets, tell her you've left your wallet in the car, go for it and don't go back. Don't have the money in your wallet, keep it in a pocket so you don't flash extra cash or cards.
Sweet Carla the Hungarian for 30 minutes is a good starting place for a new punter. Make sure you have clean socks and feet as the Hungarian girls keep their place clean by asking you to remove your shoes on arrival.